A multi-resolution mesh (MRM) is a progressive representation of a polygonal surface mesh (optionally textured) that describes a three-dimensional (3D) model. The MRM represents a mesh of v vertices as a sequence of v vertex updates. This representation permits extraction of polygonal meshes with any desired vertex count r, where 3≦r≦v, in real-time. The MRM is defined by an array of v vertex positions, an optional array of t texture coordinates, and an array of v vertex update records.
An MRM is created by iteratively collapsing one vertex of a polygon into another vertex. Although the two vertices will often be connected by an edge, occasionally also unconnected vertices are collapsed. The collapsed vertex, any unused texture coordinates, and all degenerate polygons are then removed and the texture coordinate indices of the corners of some remaining polygon are changed. Each vertex update record specifies how to undo such a collapse. Undoing such a collapse is also referred to as a vertex split.
Sending an MRM over a bandwidth-limited medium can be difficult, particularly if the MRM has a large number of vertices. This is because of the extensive amount of data that may be required to define the MRM. Compression techniques may be used in order to reduce the amount of data that defines the MRM, thereby making it easier to transmit the MRM over limited-bandwidth media.
There are several different types of information that can be compressed: the array of v vertex positions, the array of t texture coordinates, and the array of v vertex update records. Generally speaking, the largest compression gain can be achieved though a compact and loss-less encoding of the array of v vertex update records.
Like reference numerals in different figures indicate like elements.